Multiple beam radar antenna system



Feb. 16, 1965 w. ROTMAN 3,170,158

MULTIPLE BEAM RADAR ANTENNA sysTEM Filed May 8, 1963 4 Sheets-Sheet 1-LE-l N c.(6.0) e val cu/Ycn :F Focal. fue 3' l Sutra- F2.

IN VEN TOR.

WHL 76A .ea rfvnhv (fl/M IYTTOENE Feb. 16, 1965 w. Rc1-MAN MULTIPLE BEAMRADAR ANTENNA SYSTEM 4 Sheets-Sheet 2 Filed May 8, 1963 INVENTOR. WT'?kar/VHN a/w,

foe/Vfy Feb. 16, 1965 w. no1-MAN MULTIPLE BEAM RADAR ANTENNA SYSTEM 4Sheets-Sheet 3 Filed May 8, 1963 Feb. 16, 1965 w. ROTMAN MULTIPLE BEAMRADAR ANTENNA SYSTEM 4 Sheets-Sheet 4 Filed May 8, 1963 Nw y m mr e V 00 me 7 R a W n wvl MULTIPLE BEAM RDR ANTENNASYSTEM Walter Rotman,Brighton, Mass., assignor to the United States of America as representedby the Secretary of the Air Force Filed May 8, 1963, Ser. No. 279,029

l 9 Claims. (ci. 343-100) f (Granted under Title 35, U.S. Code (1952),sec. 266) The inventiondescribed'herein may be manufactured and used byor for the United States Government for governmental purposes withoutpayment to me of any royalty thereon, Y

This invention relates to directional antenna systems and relates,particularly, to radar scanning antenna systems in which a sector of airspace is scanned by a radar beam from multiple sources for detectingintruder aircraft.

One object ofthe invention is to provide a radar antenna system in whichthe comparably large mass of long range antenna structures is avoided.

Another object of the invention is the provision of a radarantennapsystem in which" the reilector illuminated by propagated energyfavorably compares in size with reflectors heretofore used.

A further object of the invention is to provide 'a radar antenna systemwherein side lobe depression of the radiation pattern is an improvementover that heretofore accomplished. Y i

A further object of the invention isutheprovision of a radar antennasystem wherein greater scanning speeds l United States Patent angleotthe aircraft detected is determined by phase comparison betweencorresponding inputs of reected energy returned to the two lens systems.

Complete understanding of the invention and introduction into otherobjects and features' not specically mentioned may be had from thefollowing detailed description of several specific embodiments thereofin conjunction with theappended drawings in which:

FIG. l is a plan view of the lens arrangement embodied in the radarantenna system of the invention;

FIG. 2 is a view partially in section taken along line 2-2 of FIG. l;

may be employed with the resultant improvement Vof a i largersectorscanned; q

Yet another object of theinvention is the provision of a radar antennasystem wherein the peak power require-v ments are reduced tolevelsfavorable for lengthening the operating life of the systemcomponents. To accomplish the foregoing, objects, in a systemconstructed in accordance with the present invention, a number of wavesof electromagnetic energy are generated withdiscrete angular spacingsand scanning is accom- -plished by varying electricalpath lengthsencounteredby each of the waves in a phase shifter bank. vThe 'waves areshifted fromrtheir unperturbed paths over Lan angular intervalsufficient to cover theY entire field of view assigned for radarcoverage. Structural characteristics pertinent to the radar antennasystem of the inventionV include a parallel plate transmission line fedby multiple stationary inputs of electromagnetic energy each of whichis-'capable of generating a beam in a different angular direction, a

two-dimensional-lens connected to probes which extract FIG. 3 is a raytrace diagram showing certain parameters of the lens construction;

FIG. 4 is a view in perspective showing the lens arrangement of FIG. lilluminating a typical reflector;

FG. 5 is a perspective View essentially of FIG. l with phase shiftingmeans inserted; and

FIGS. 6 and 7 illustrate alternative embodiments of the inventionemploying the basic structure shown in the antenna system of FIG. l.

Referring to the drawings, in which like reference characiers refer tolike elements in each of the several views, in FIGS. l and 2 there isshown one embodiment of a microwave lens radar system constructedaccording to the invention. Reference character 10 generally designatesa parallel plate microwave lens comprising two parallel plates 12 and 14open at one end to present a feed aperture 16. The lens axisbisects theparallel plates in the longitudinal direction. Microwave radiation fromprimary horn illuminators 1S, located along the aperture 16, propagatesbetween the parallel plates toward pickoft probes Ztl disposedadjacent-the other end of the paralllel plate region. Probes 20 extractthe energy from the the parallel plate region over a wide range ofincident feed angles. In the followingwformulation of the designequations for the microwave lens, reference is made to .50Qtransitionsbetween the parallel plates yand the coaxial energy from the parallelplate region, a bank of'phase shifter elements exposed to the inputenergywrhose electrical path lengths can be varied, and a linear Yarrayof radiating elements fed individuallyby the phase shifter elements forradiating the energy into space. The radiatf ing 'elements achieve abroadside radiation pattern used for illuminating a shapedcylindricalparabolic lrelector whch'narrows-the beam inthe orthogonal plane.

According to another V'feature of the invention, the

FG. 3 in which parameters unique to the lens construction of theinvention are illustrated.vv In FIG. 3, the lens surfaces are showntwo-dimensionallyby the cross sections El and 22. The first contour, 21,defines the inner lens' surface 'and determines the' position of the`probe lines. The second contour, 22, is the outer lens surface and isdefined by the location of the radiatingelements that comprise the linesource. Corresponding elements on contours'El. and 22 are .connected bya coaxial trans- Vmission line 25; The third contour is the circularfocal arc which is selected as a segment of a circle whose cen- ,f terlies on the lens4 axis and which passes through the onmicrowave lensformed by the parallel plate transmissionv line is replaced by ageodesicspillbox having` wide angle i. t

`scanning properties.

An' extension of the basic lantenna structure embody-V 4ing theinventionrtoobtain instantaneous vheight-finding` information Ybyphase-'comparison techniques formsz a1" third feature of the finvention..ll-lere, beams separated 'from each other by `a predetermined angle areemitted .simultaneously for thelpurpos'e of determiningthe elevation.angle of the intruder aircraft.v -In Vsuch an embodiv ment,two'identical banks of `identicalphase shifting elements and wideganglevlensesare required. `The elevation g, k

vaxis focal point and two symmetrical olf-axis points.

` A point on the contour El is` defined by the two coordinates (X,Y)'that are measured relative tothe vertex of the lens at O1. Points onthe straight contour Z2 are similarly determined by the Vsinglecoordinate N, measured relative to the point G2 on the axis. The points01 and O2 lie on contours El and-Z2` respectively and are Vconnected bya coaxial transmission line 2d of electrical vlength W0. The pointl,defined bythe coordinates X and Y, is a typical probe element in El andis connected l.

to point Q, which lies on 22 and is defined by the coordinate N, by thetransmission line 25 of electrical length W. The three quantities X, Y,and W can be Vchosen at will; thus this straight-front-faceV lens hasthree degrees of freedom.

The lens is now designed so that the three focal points F1, F2, and G1give perfectly collimated beams of radiation at angles to the axis offa, `la, and 0 respectively.

Equations for the optical path-length conditions for path-lengthequality between a general rayand the ray P1P, P2P, and GIP representpath lengths from focal points F1, F2, and G respectively to the innersurface of the lens.

Norinalizing relative to the focal length F defines a new set ofparameters:

Equations la to 3a may then be written:

y Equations 3 and 3b, relating to the on-axis focus, may likewise bewritten:

Equations 5 and 6 can be lcombined to give the following relationbetween w and p:

er1-pesan where Equation 7 is a quadratic equation in w whose solutionis:

- b -I- w/b2 lac 2a This completes the solution for the lens design. Forfixed values of or and g, w can be computed as a function of p fromEquation 7. rhese values vof w and p may then be substituted intoEquations 4 and 6 to determine x and y and complete the specification ofthe lens dimensions.

The design procedure, as outlined hereinabove, gives a lens which .hasthree perfect focal points corresponding to the angles in: and 0. Forwide angle scanning the focusing ability of the lens must be'acceptablenot only at these three points but also at intermediate angles alongsome focal are. In order to illustrate how further to minimize theoverall phase aberrations it is helpful to consider parameter g ingreater detail. It will be recalled that g is the ratio of on-axis focallength G to off-axis focal length F. For the special case of a straightface at the outer surface of the lens, as is shown herein, the criterionrelied on is thatrminimum coma and overall phase error is obtained bydefocusing the feed from the assumed focal arc by'an amount equal to1z(ot2-9Z)F, where 0 is the intermediate angle at which correction isdesired. With this defocusing the residual. aberrations are quite smalland the lens can scan a narrow beam over wide angles. The optimum valueof g for aberration reduction equals The focal aro is now selected as asegment of a circle of radius R, whose center lies on the lens axis andwhich passes through the two symmetrical off-axis points F1 and F2 andthe one on-axis focal point G1. The phase error from any point on thisfocal. arc (expressed as the difference in path length between thecentral ray and any other ray) may be shown to be:

As an illustrative' example the equation will be applied to obtainnumerical solutions pertaining to the lens design. `A total scan angle,2a, between the off-axis points F1 and F2 is selected as 60. Thefollowing parameters are immediately determined:

dij-:30 a0=eos @1:08650 b0=Si11 11:0.5 y? 1+ (COS 0:)2

` 0. l. 0. 0000 0. 0000iV 0. 0000 0. 0000 0. 2 0 0000 0. 0000 0. 0000 0.0000 0. 3 0. 0000 0. 0000- 0. 0000 0. 0000 0. 4 0. 0000 0. 0000 0. 00000. 0000 0. 5 0. 0000 0. 0000 0. 0000 0. 0000 0. 6 0. 0002 0. 0003 0.0003 0. 0002 0. 7 i 0. 0010 0. 0014 i 0. 0015 0. 0012 0. 75 0. 0020 00028 0. 0031 0. 0024 Substituting these values in the relations 4ofEquation 7A gives in terms otp: i

Representative values of x,y, andw computed from Equations 4, 6 and 7 asa function of p, and over a range .7 5 p 0 with an interval. of 0.1, aregiven in the `follow- The radius R of the focal arc'for a lens of.g4-:1.137 has the dimensions of 0.59 7Fj and its Origin on the axis is0.15403F from the Vertex O1.

From Equation 9, the path lengthphase error Al can be determined forfvariou's values of the scan angle 6. It Willbe understood that for 19:0and i30", Al iszero.

`The `following two tables are tabulations of the path lengthphase'error nl for 6=il0, $15", i20, and i25 and Since the` directivityof .each horn illuminator 18 is afunction of its positions along thefocal arc relative tofthe lens axis, the dimensionsof each horn and itsOrientation depends on'its position. Also, the peak of radiation neednot, in general, be in the directionof the vertex of the lens. Thus, fordifferent directions in space the-angular movements of various .beamsVVusually will not be identical for a'given amount of phase shift. Ac-

` cordingly, to derive the equations for theshift Vinlbeam positionandto determine the location of the feedsto obtain complete coverageofthe field of view, let the following notations be assumed: @n-angularposition of nth feed in the lens relative to `thelensaxis m q n=angularposition Vin space of radiated be'am from nth feed. 1 d=spacing ofradiating elements in linear arrays, ex-

pressed in'wavelengths. 1 t =additional phase shift'in wavelengthsarticially in- -1 troduced between adjacent radiating elements(` For,`l-=0, the angular positions of the beams, pn, correspondsv to that ofthe feeds, 6m Theproblem may now be restated; Given N feeds, determinetheir angular is introduced by adding ya phase shifter between theoutput ends of the coaxial transmission lines and the array of radiatingelements to which they attach. The beam moves to a new position givenby:

Eachubeam must movefromits position Pn to position n`+1 in order toobtain complete scanning coverage.V

d; N And the positionof the nth feedis at: A

@asnifm mlianaa.- sin 0.)] in positions ofthe beam.

In themicrowaveV lens Vradar system shown in FIGS. 1 and 2, theradiation patternV from the array of radiators iis, in a practicalsense, much too broadto be `directly propagated into space for largerange detection purposes.

Accordingly, as shown in FIG. 4, a parabolic cylindrical' reilector forcollimatirig the beam in elevation may be employed. As appears in FG. 4pa parallel plate transmission lineilt), identical to the constructionshown in FlG.' 1,A comprisesa pair of parallel plateslZ and 14 l and isfed at one end by input `horns 18 having-connec tions tosuitable`ftransmi'tting and receiving translating apparatus. Atthe otherend of the plates are pick-olf probes: Z0` spaced Vfrom eachother'onropposite sides of thelens laxis in` accordance with theequations set forth hereinabove. Alinear array of radiators 34 receivesits energy from the pick-o probes through Suitable coaxial transmissionlines 36.

In transmission, input sources (not shown) connected to horns 18 emitwaves of electromagnetic energy which is directed intro the apertureV ofthe parallel plates, with the p ath'of each beam after leaving theradiators 34 being des terminedjby the position of the .horn illuminatorwhich generates it. Microwave energy .taken by the pick-olf probes fromthe parallel plate region 'is conveyed over coaxial transmission lines36 to illuminate Va parabolic cylindrical reflector 31. The shape ofreflector 31 is to narrow the beam in the orthogonal plane. The systemsof FIGS. 1, 2 and 4 will, of course, include suitable means leading fromthe feed horns to use energy returned from detected intruder objects fordetermining pertinent tracking information.

In the above description of the parallel plate microwave lens it wasnoted that beams from the radiating elements are radiated in differentfixed directions corresponding to the orientation of the feed horns.FIG. shows an arrangement, in accordance with the invention for scanningthe multiple beams. In FIG. 5 a parallel plate microwave lens systemcorresponding essentially to the system identified by FIG 1 is modifiedby inserting in series with the coaxial transmisison lines 36, a phaseshifter generally indicated at 3S which introduces a linearlyprogressing phase shift'between successive lines. The

trombone type phase shifter is acceptable for usein the presentinvention and, as herein shown, each phase shifter comprises upper andlower portions 4t) and 42, respectively, of telescoping tubing whoseadjustment relative to each other changes the path length of theindividual phase shifter. The two halves of each lower section 42 arejoined by a U-shaped connector 44, only one being shown for simplicity,which fixedly connects each lower section to a bar 46. The angle of bar46 relative to a fixed plane is made adjustable by virtue of a hingeconnection 4S at one end of the bar. A single aperture elongated horn 50forms the radiator. The electrical wave condueing path between theoutput end of each coaxial transmission line 36 and the aperture 52 ofhorn Sil is traced downwardly through one of the halves of the section40 and through the` lower section 42 and thence upwardly through theother half by section 40 to aperture 52.

In operation, when microwave energy is applied to horn illuminators 18,passage of the energy to the aperture of radiator 50 produces angularlyrelated multiple beams. Moving bar 46 about point 48 causes anadjustment in the length of each phase shifter and a proportionate phaseshift of the energy conveyed by each phase shifter. The progressivephase shift as 4the bar moves causes the desired scanning of the beamsby angularly shifting the positiony of the main lobe of the radiationpattern resulting from each beam. For ease in illustration, a reflectorilluminated by the scanning beams is not shown. Moreover, a suitablemechanism coupled to bar 46 for achieving the scanning requirements willreadily occur to those skilled in the art and hence is not shown. Thelower section of each phase shifter is initially adjusted to assure ascan of each beam of several degrees over a limited sector of space.Thus, as the wave energy of each beam encounters the phase shifterelements it will be swept over a limited sector sufliciently to causeyoverlapping of the undeflected azimuthal directions of the respectivebeams. It will thus be `understood that the' entire field of view may becovered by several independent beams each of which covers only a portionof the region under surveillance. It has been shown that the gain of anarray of radiating elements when arranged in the manner of the inventionremains fairly constant during the transitions of the beams over theassigned sector and thatV the shape of the radiation pattern resistsdeterioration even at relatively large angles of deflection.

A principal advantage of the reflector-lens combination shown in the`arrangement of FIGS. 1 and 2 and the modified version of FIG. 5 is thealmost complete lack of aberrations. For a scan angle of i 30computations show that the aberrations are nonexistent to threesignificant figures when the focal length is normalized to unity.Expressed in terms of the practical benefits secured, the entireaperture of the parallel plate lens and the line source of radiatingelements feeding the reector may be-used to collimate the beam A typicallens-reiiector installation constructed accordbetween and 100.

ing to the embodiments shown and using a fixed directional refiector mayhave the following parameters:

Scan angle l30 Beam width l x 1 Line source 190 ft. long Parabolicrefiector 210 ft. long x ft. high Aside from having exceptional wideangle scanning properties, the antenna systems of the invention has thedefinite advantage of longer service life. This follows by employingseveral transmitters each operating on a relatively low power leverrather than using a single transmitter unit having high powerrequirements. Consequently, problems are eased in the case offabrication, installation and maintenance of the transmitters. Alsoreduced considerably is theY steady deterioration of system componentsfelt ordinarily under high power conditions of single transmittersystems. For the same total average power and phase shiftingperformance, each of the horns of the line source of a singletransmitter system must be capable of withstanding higher breakdownvoltages than for a multiple beam systemY of the type embodying theinvention. The total RMS. voltage (given by the square root'of the sumof the square of the voltages produced by the individual transmitters)is thus lower in each part of a multiple beam system than in a singlebeam system. It follows that a given component in the antenna system ofthe instant invention can handle a higher average power level for themultiple transmitter system if breakdown voltage is the limiting factor.

The use of a multiple beam arrangement also tends t0 reduce the scanningloss which ordinarily occurs in a single transmitter system. Losses insingle transmitter systems are due to movement of the beam duringscanning before the reflected pulse from the target returns to thereceiver. The scanning loss is a function of the scan rate of theantenna and, also, is related to the distance to the target. Inthemultiple beam system of the present invention, each beam is able tomove more slowly to obtain a given frame scan rate. Conversely, theframe rate can be increased forV a given scanning loss.

Recent calculations Ahave shown that lenses may be designed with a=i45for a total useful scan angle of The 60 sector lens was selected forillustrative purposes and is not intended to represent a limiting case.This feature of the invention is embodied in the arrangement of FIG. 6.In FIG. 6, a geodesic pillbox wave conducting medium referenced 54consists of two semicircular parallel plates 56 and 57 of differentdiameter open along the diameter edges 4thereof to present .an aperture58 of constant height. Mounted on the curved edges of plates 56 and 57and of corresponding diameter are semi-circular geodesic pillboxsurfaces 58 and 60 which together enclose a curved linearly spacedregion extending downwardly to communicate with the space between theparallel plates. Energy due to an applied electric field from a suitablemicrowave power source is propagated between plates 56 and 57 -by meansof input feed horns 62 supported in spaced Irelation on the rim joiningsurfaces 58 and 60. The aforementioned construction thus affordsmultiple sources of radiation each capable of emitting a beam in aspecified direction between plates 56 and 57. In the most simple terms,the design of the pillbox 54 is based upon the wide angle scanningproperties of a semicircular recctor combined with vertical geodesiccontours for the purpose of reducing spherical aberration. While thetype of geodesic pillbox contemplated for use in the arrangement of FIG.6 has much less spherical aberration than a nonge'odesic system, theaberrations which occur are still too great to permit formation of beamsas narrow as 1 efficiently. Accordingly, collimated energy appearing 'atthe output layer of geodesic pillbox 54 due to the infiuence of anapplied electric field is extracted by a series'of closely spacedpick-off lines 63 located along the diameter of the lens. Energy thusremoved by the lines 63 is led to a bank of phase -shifters 64 composedof a plurality of individual phase shifters each connectedto receive theinput from one of the pick-oliC probes. The output of the bank of phaseshifters 64 is fed by means of transmission cables 65 to a linear arrayof horn radiators 66 which comprise a line source for a cylindricalparalbolic reflector 67 supported by suitableposts 68. The relativephase delay produced by the phase shifters serves to scan the individualbeams, which illuminate the reflector 67, in the manner previouslyexplained for ythe microwave lens design.

The physical dimensions of the antenna system embodied in the FIG. 6arrangement are almost identical v tion angle of the target aircraft andis preserved through"V the remainder of the antenna system. n In FIG. 7,twoidentical parallel plate lenses 69 and 70 are superimposed inparallel relation to receive the micros wave energy from the twoterminals of the waveguide array 78 after passage through identical andsynchronized banks 75 and 76 of phase shifter elements by means oftransmission cables 73 and 74. The manner of operation of the lenses andphase shifters has been described hereto those of the flat parallelplate lens systems hereinabove 'Y described with the exception that thetotal scan angle achievable is about 100 instead of 60. By placing theparabolic reector between the array of radiators and the pillbox care istaken that the radiation pattern from the reflector 67 is directed awayfrom the pillbox itself since the considerable height of the verticalsurfaces'58 and 60 could cause shadowing. No significant shadowvingoccurs inthe radar antenna system of the invention using the parallelplate lens because of-the at surfaces Since in radar applications it isdesired to scan a narrow beamover, a wide angular region, thecylindrical parabolic reflector illustrated in connection with each ofthe4 previously described embodiments more than adequately serves thispurpose. Thus, in practical arrangements, line sources suitable .toilluminate a cylindrical parabolic reflector or other suitable lens willordinarily be employed.

VV,Also inaccordance With a feature of the invention,

VFIG. 7 discloses a multiple beam radar antenna for determininginstantaneous solutions to theheight of an intruder aircraft` entering-anY assigned area by comparing the 'phase of return echoesfrom-thetarget as received at fthe `terminals .of two identical parallelplate lenses. Y f Ihus, as shown in FIG. 7, the principle ofthe'parallel plate lens and parabolic reflector previously discussed ini connection with FIGS. 4 and 5 is retained and'extended to obtain theheight finding *function* It is assumed in the 'following discussionthat the intruder aircraft is illuminated by some suitable microwaveVradar transmitter and that the radar antenna of FIG.4 7 is used forrecepinabove and will not he repeated. Thus, the microwave energy whichis reflected from the target aircraft is received at an appropriate setof feed horns 71 and 72, and at a period during the scan cycle which isdetermined by theV azimuthal position of the target. Suitable receiverequipment 86 for instant phase determination is connected between feedhorns 71 and 72 and give appropriate outputs for elevationdetermination. Simplification of target identification and trajectoryprediction follows from the phase comparision method of heighiinding.

In the several embodiments of the invention shown, the spacing of thepick-off probes and the radiating elements included in each antennaarray should be yclose enough together to prevent secondary beams fromoccurring; for the range of angles desired, a spacing of about 0.65K issatisfactory, where is the wavelength of the operatingV frequency.Moreover, to obtain completeY coverage ofthe assigned eld of view ineach embodiment of the antenna system described hereinabove, it is notedthat the total phase shift required of each phase shifting unit is onlyl/N of that nccesary to scan a single beam over the entireeld, WhereNYequals the number of feed horns.

.It will be apparent to those skilled in the artthat `changes' andmodifications of the several embodiments of the invention illustratedAand described may bemadetheretion only.' .i The transmitted radiationcan be vobtained i Y either from a `separate and synchronizedantennalsystem or by time-sharing and switching portions YofItl'ie're'ceiving K antenna system of FIG. 7 for transmission purposes.

`Microwave energywhich is reected'from vthe intruder, Y'

Y aircraftwill be incident upon the cylindrical parabolic re-V A, lector80,` shown in FIG. 7, in the form of-a-planel wave whose angle ofincidence -is dependent upon the elevation ofthe target aircraft.

This radiation is focused along a line upon the waveguide array.composed of a plurality of two-terminal slotted waveguides 78whicharellocated -along the focal Aarc of the vcylindrical reflector 80. The

p `position along the slotted waveguides 78 at which Vthe 1l energy isfocused is a function of the angle ofincidence of the incoming radiationand of, hence, target elevation. For simplicity in illustration, thewaveguides'78A are 1 herein shownfdiagrammaticall'y since theirexactform'is not material to the invention; aslotted waveguide whichcould be used in FIG. 7 is shown in Radiation Laboratory Series, vol.v12, pages 287 and 296. Briefly, a slotted waveguide ofthe typeconsidered constitutes a series of equispaced slotted radiative elementsand a supporting waveguide transmission line. The microwave radiationfrom `the cylindrical reflector 80 enters the waveguide 78 princ ipallythrough single one of thev slot radiators whose the scopel of theappended claims.

I claim: v y 1. Aradar antenna systemcomprising, a parallel plate waveconducting lens having a feed aperture, `multiple beam producing meansfor launching a plurality of wave energy beams separated angularly fromeach other relative to the lens axis into the aperture of said lens,"alinear array'of radiating elements, vand multiple phase shifter meansreceiving the energy propagating within saidilens and coupled in energyconducting relation tov said array of radiating elements for linearlyaltering the phase shift :of the'energy input into said array thereby toscan the i s radiated energy.` through va predetermined space.

y2. In combination, ka parallel plate lens at `one end havinga curvedaperture symmetrical on each side of the lens axis, point sources lofwave energy differently angularly related tothe lensa'xis forilluminating said aperture, Y Y vprobe meanscoupled to the opposite endof said lens for extracting Wave energy propagating therein, a lineararray of radiatiang elements, and phase shift means connected to saidarray receiving the energy so extracted by said probe means forsynchronouslychanging the velocity of said Y energy wherebyeach beamemanating from said radiating position is determined by. the elevationangle of the tar--v l i get. Thisgmicrowave energy propagatesfin bothdirections withinthe waveguide 78 `and arrives 'Vat its twoter' A lminals with -a-relative .time delay orphase-shift which is dependentupon the positionof the illuminated slot.' This relative difference inphasebetweenjthe signals at'the two terminals canbe interpreted intermsy of the elevaelements scans through a preselected fraction' of apredetermined space.

coupled to said plates to communicate with said aperture,

each of said sources generating abeam directed in a different angulardirection relativeto the lensaxis, probe means coupled to said platesfor extracting energy propagating between said plates, a linear array ofradiators oriented to deliverla narrow-beam pattern inV space, and

phase shift means interconnecting said probe means and said array ofradiators for introducing a linearly increas- 3,170, i es ing phaseshift in the phase vof theenergy transferred from said lens to saidarray.

4. A radar antenna system comprising two parallel plates forming aparallel'plate lens having a feed aperture at one end thereof,symmetrical focal arc surfaces formed at both ends of said plate withthe centers thereof falling on the lens axis, plural sources ofelectromagnetic energy located adjacent said aperture at regularintervals apart and directing into said aperture multiple kbeams of waveenergy angularly related to the lens axis, an array of radiatingelements linearly arranged to form a line source of radiation, pluralphase Shifters each connected to one of said radiating elementsaccording to a predetermined pattern and being so phased that waveenergy received by said phase shifters emanates from said radiatingelements as multiple beams scanning through a predetermined angle, andprobe means coupled to the opposite end of said plates for extractingwave energy from said lens and conveying the energy so extracted to saidphase Shifters.

5. A radar antenna system comprising a parallel plate lens includingspaced parallel vplates closed at one end and having a curved apertureat the opposite end of a curvature defined by the focal arc of the lens,multiple stationary means having different angular positions relative tothe lens axis for individually applying wave signals into said aperture,probe means coupled to the closed end of said lens for extractingtherefrom energy of said wave signals, said .probe means each comprisinga coaxial cable having an inner conductor conveying the energy soextracted to a point external to said lens and an outer conductor inelectrical contact with said plates, a plurality of phase shiftelements, a linear array of radiating elements disposed to present anarrow-beam pattern in spaced upon excitation thereof, and `means forcon: necting each of said phase shift elements between one of saidradiating elements `and one ofthe inner conductors of said coaxialcables and said phase shift elements being so adjusted as to excite saidradiatingelements in proper phase to scan simultaneously multiple beamsthrough a predetermined space. 4

6. A radar antenna system as claimed in claim 5 wherein a reflector fornarrowing an incidentbeam in the orthogonal plane is illuminated by thebeam emanating from said array of radiating elements.

7. A radar antenna system as claimed in claim 6 wherein said rellectoris a cylindricalparabolic section.

8. A radar antenna system comprising a geodesic'pillbox including twosemicircular parallel plates of different diameter open along the.diameter edge thereof to present an aperture of constant height andtwo' semicircular geodesic surfaces mounted on the curved edgesv of saidparallel plates to enclose a curved linearlyspaced region communicatingwith the space between said plates, means for injecting wave energybetween said geodesic surfaces so as to illuminate said aperture withcollimated energy, a plurality of closely spaced probes coupled to saidpillbox along the diameter of said plates, a plurality of phase shiftingdevices, coaxial cables for connecting each of said probes to one of thephase shifting devices, a plurality of radiating elements each fed byone of said phase shifting devices and said radiating elements beingdisposed in a linear array to present a broadside pattern of radiation,and a cylindrical parabolic reflector disposed for illumination by theenergy emanating from said radiating elementssaid phase Shifters eachintroducing a linear phase shift between the pillbox and said array ofradiators whereby the resulting radiation reflected from said reflectorscans through a predetermined space.

9. A radar antenna system for determining the height and other spatialcoordinates of an intruder aircraft entering .the space designed forradar coverage comprising: a cylindrical parabolic reflector disposed toreceive 1 reflected wave energy when target aircraft is illuminated t byan external transmitting source, a plurality of twoterminalslotted-waveguide units upon which the energy received by said reflectoris focused, the focal position depending upon elevation of targetaircraft, each waveguide unit including multiple superposed slots, saidslots being so oriented that upon reception of waves from saidcylindrical reflector signals are available at the two terminals of eachwaveguide unit with a relative phase relation which corresponds to theelevation angle of target aircraft, two banks of phase shifter units,each phase shifter being connected to one terminal of said slottedwaveguide unit, said banks of phase shifter units each introducing alinear phase shift and corresponding angular shift in wavefrontofreceived signals from said slotted waveguide unit for determiningazimuthal position of target aircraft, two superposed parallel platelenses disposed in parallel relation with electrically separate probemeans connected to one end thereof for extracting wave energy whichpropagates through said phase shifter units, the opposite end of saidlenses having a feed aperture of con-` stant height for lreception ofincoming signals by individual horn means, and receiver means alsocoupled between said horn means for comparing the relative phase ofreflected energy returned from said aircnaftthrou'gh said antenna systemwhereby the height of said aircraft may be determined.

References Cited by the Examiner l UNITED STATES PATENTS 2,566,703 .9/51Iams 343-100 2,736,894 2/56 Koele 343-4911 3,0l6,53l l/62 Toiniyasu etal. 343-122 CHESTER L. IUSTUS, Primary Examiner.

1. A RADAR ANTENNA SYSTEM COMPRISING, A PARALLEL PLATE WAVE CONDUCTINGLENS HAVING A FEED APERTURE, MULTIPLE BEAMS PRODUCING MEANS FORLAUNCHING A PLURALITY OF WAVE ENERGY BEAMS SEPARATED ANGULARLY FROM EACHOTHER RELATIVE TO THE LENS AXIS INTO THE APERTURE OF SAID LENS, A LINEARARRAY OF RADIATING ELEMENTS, AND MULTIPLE PHASE SHIFTER MEANS RECEIVINGTHE ENERGY PROPAGATING WITHIN SAID LENS AND COUPLED IN ENERGY CONDUCTINGRELATION TO SAID ARRAY OF RADIATING ELEMENTS FOR LINEARLY ALTERING THEPHASE SHIFT OF THE ENERGY INPUT INTO SAID ARRAY THEREBY TO SCAN THERADIATED ENERGY THROUGH A PREDETERMINED SPACE.